JP5929955B2 - Powder for clothing mass - Google Patents

Description

  The present invention relates to an agglomerated powder, and more particularly to an agglomerated powder for use in ingot casting of molten metal by a clothing ingot method.

  Ingot casting, in which molten metal is poured into a mold and solidified to obtain a slab, is used for ingots of various metals. In particular, even today, when continuous casting is generalized, there are many special steel types that are difficult to continuously cast, and it is required to obtain slabs with high cleanliness by ingot casting. Ingot casting includes the upper pouring method in which molten metal is injected from the upper part of the mold and the lower pouring method in which molten metal is injected from below the mold through a refractory runway. In general, the bottom pouring method is applied. In the down-casting method, an oxide-based material that forms molten slag by receiving the heat of the molten metal may be added in order to suppress the reforming of the ingot slab and the generation of defects. Since such an additive is usually in a powder form, it is called an agglomerated powder. One of the roles of the agglomerated powder is a coating material. The coating material is melted by receiving the heat of the molten steel to form molten powder slag on the surface of the molten metal in the mold, which is effective for heat retention, oxidation prevention, absorption of inclusions, suppression of blowhole generation, and the like.

  Furthermore, the agglomerated powder is placed in the ingot casting mold, and the molten powder slag formed on the surface of the molten metal when the molten metal level in the bottom pouring ingot is raised, is changed between the molten metal and the mold when the molten metal level rises. There is a method in which a film of molten powder slag is formed between the side surface of the metal slab and the mold. In this method, the slab is wrapped like a garment with a powder slag film, and since the surface property of the slab is excellent, it is called a garment ingot method. In the clothing ingot method, the molten powder slag film formed between the side surface of the metal slab and the ingot mold fills the unevenness of the inner wall of the mold, so that a clean ingot having no unevenness on the side surface of the slab can be obtained.

As an agglomerated powder used in the ingot-making method, for example, in Patent Document 1, SiO ₂ is 35 to 60%, CaO is 10 to 25%, and Al ₂ O ₃ is 4 to 8% as a main component. Disclosed is an ingot casting method characterized by interposing a plate-like material contained between a powder coating and a molten steel surface, and performing molten steel casting. Examples include ₂ 35 to 65%, CaO 10 to 25%, Al ₂ O ₃ 4 to 8%, R ₂ O _{10 to} 15%, CaF _{2 2 to} 6%, and carbon 2 to 20%. In Patent Document 2, in a method of pouring molten metal from a ladle into a mold installed on a surface plate, a plate-shaped molten metal coating material and a powdery coating material are installed in the mold. In addition, a pouring and ingot casting method is disclosed, in which the powdery coating material is placed at the lower part of the plate-shaped molten metal coating material and ingoted, and the same document discloses an example of the powdery coating material. Graphite powder 1 against 90% of a powder obtained by pulverizing a mixed melt of SiO ₂ 50%, CaO 10%, B ₂ O ₃ 20%, CaF ₂ 10%, Na ₂ CO ₃ 5% and K ₂ CO ₃ 5% The thing which added and mix | blended the crack is described. Further, Patent Document 3 discloses an ingot manufacturing method characterized in that molten steel is filled in an ingot mold having an inner surface lined with ceramic paper, and the ingot is manufactured. Describes a molten slag of the ingot method of SiO ₂ 34%, CaO 31%, Al ₂ O ₃ 2%, NaO 14%, MgO 5%, F9%.

JP 52-151627 A Japanese Patent Application Laid-Open No. 59-130684 Japanese Patent Laid-Open No. 62-9746

  However, in the garment ingot method, the powder slag film covers the surface of the slab and makes the surface property of the slab excellent, while the powder slag film adheres to the surface of the slab. In addition, since the powder slag film remains firmly attached and remains on the surface of the slab even after the slab is cooled, it is necessary to perform a removing operation of the powder slag film before rolling, and the process becomes complicated. Furthermore, when the removal of the powder slag film is not complete, there is also a problem of causing a rolling defect in the rolling process.

  Therefore, the object of the present invention is to solve the problem that the powder slag film of the powder for clothing ingot used in the clothing ingot method adheres firmly to the surface of the slab and omits the powder slag film removing operation. It is to simplify the work process and prevent rolling defects in the rolling process.

That is, in the powder for clothing ingot, the present invention has a composition represented by the oxide equivalent amount of the molten powder slag obtained by heating the powder for clothing ingot to 1300 ° C, CaO: 30 to 70 mass%, SiO ₂ : 0 to 25% by mass, Al ₂ O ₃ : 20 to 45% by mass and Na ₂ O + Li ₂ O + F + MgO: 10 to 30% by mass, and after heating at 1300 ° C. for 10 minutes, when cooled to room temperature A powder for clothing ingot, characterized in that calcium oxide crystals, dicalcium silicate crystals, or both precipitate as crystal phases in the cooled molten powder slag.

  Moreover, the powder for clothing ingots of the present invention is characterized in that the sum of the amounts of calcium oxide crystals and dicalcium silicate crystals is in the range of 5 to 20% by mass in the cooled molten powder slag.

  Moreover, the powder for garments of the present invention is characterized in that the molten powder slag has a viscosity at 1300 ° C. in the range of 0.01 to 20.0 Pa · sec.

The batter ingot for powder of the present invention, the powder slag film formed between the cast piece and the mold, powdered before the next step, by applying a decay characteristic, the residual slag to the slab surface It is possible to prevent the slag removal work from being omitted and to eliminate defects caused by the powder slag film in the rolled product.

The inventors of the present invention have studied various methods for easily removing the powder slag film from the slab in the garment ingot method.
In the clothing block method, it is considered that the molten powder slag is cooled by a cooled mold to form a powder slag film, and a solidified metal shell is formed on the inside. Since the interface between the powder slag film and the solidified metal shell is a free surface, the interface is extremely clean and smooth. Therefore, it was estimated that the solidified metal shell and the powder slag film adhered firmly.

  On the other hand, since the thermal expansion coefficient of the metal solidified shell and the powder slag film are different, a shrinkage difference occurred during cooling, and it was expected that peeling would occur at some interfaces, but actually it did not peel, It can be determined that the effect of the shrinkage difference is not great. If this cause is estimated, in the powder for agglomeration as described in the above-mentioned patent documents 1 to 3, it is considered that the powder slag film is composed of silicate glass and a part of crystal phase. However, the glass phase is softened and deformed at a high temperature in the initial stage of solidification, and the thermal stress generated by the difference in expansion is relieved.

  Therefore, for example, if a large volume change can be positively caused in the powder slag film in a low temperature range such as 900 ° C. or lower, the powder slag film can be easily removed from the slab. Examples of the crystal phase exhibiting such actions and effects in the powder slag film include calcium oxide crystals and dicalcium silicate crystals. Calcium oxide crystals react with water vapor in the air to produce calcium hydroxide and have a volume expansion of about 50%. In addition, the dicalcium silicate crystal undergoes a phase transition from α′-type to γ-type at a temperature range of about 850 ° C. or less, resulting in a volume change of about 11%. In cement and steel slag, it causes a phenomenon of powdering. It is known that. It was considered to remove the powder slag film from the slab using such volume change.

Therefore, the powder for clothing ingot was melted under specific conditions to create a molten powder slag, and a cooled powder slag was produced by cooling it. The composition of the agglomerated powder was appropriately changed by trial and error so that calcium oxide crystals or dicalcium silicate crystals exist as crystal phases in the cooling powder slag.
First, the method for producing the molten powder slag was examined, but it was found that melting at 1300 ° C. for 10 minutes coincided with the conditions of the actual machine. Heating was performed in an electric furnace, and graphite was used for the crucible. The sample was suddenly inserted into the furnace at 1300 ° C together with the crucible. The heating temperature of 1300 ° C. is generally based on the knowledge that melting at 1300 ° C. is a temperature suitable for reproducing an actual machine. The heating time was 10 minutes. When the heating time is short, the powder slag is insufficient and the actual machine cannot be reflected. In addition, heating for a time exceeding 10 minutes is not preferable because the powder component partially evaporates and the component changes.

  The crucible used for melting the powder for clothing ingot is not particularly limited as long as it is a material that does not substantially react with the molten powder slag. In the experiment, graphite was used, but platinum or the like may be used.

  In addition, the cooling is performed by cooling in the furnace, or after being taken out of the furnace, it is naturally cooled to room temperature. The cooling rate is preferably 20 ° C./min or less, more preferably 10 ° C./min or less. When the cooling rate is too high, unlike the actual machine conditions, the slag is vitrified, which is not preferable.

  The amount of calcium oxide crystals and dicalcium silicate crystals in the cooling powder slag was determined according to the internal standard method of JIS K 0131 “General Rules for X-ray Diffraction Analysis”. The relationship was examined. As a result, when the sum of the amount of the calcium oxide crystal phase and the amount of the dicalcium silicate crystal phase is 5% by mass or more, the cooling powder slag cracks during cooling and storage, and collapses when it is significant. I was able to confirm that.

  That is, the sum of the amount of calcium oxide crystals and the amount of dicalcium silicate crystals is preferably in the range of 5 to 20% by mass, more preferably in the range of 10 to 15% by mass. When the sum of the amount of the crystals is less than 5% by mass, the amount of volume expansion is small, and the removal of the powder slag film from the slab does not easily occur, which is not preferable. On the other hand, if the sum of the amounts of the crystals exceeds 20% by mass, the melting point becomes excessively high, which may cause poor melting.

  Furthermore, when this garment ingot powder is applied to an actual machine, it can be confirmed that the powder slag film formed on the surface of the slab is easily removed, and the present invention has been made based on this discovery. .

  The slag film formed in the actual operation in the clothing ingot method is air-cooled to the vicinity of room temperature in the atmosphere in a state of adhering to the surface of the slab, and in some cases water-cooled by watering. Cooling typically takes several days or longer. In this condition, it is important that calcium oxide crystals and / or dicalcium silicate crystals exist in the slag. As described above, the calcium oxide crystal is digested by moisture in the atmosphere and expands in volume, and the dicalcium silicate crystal expands in volume due to a phase transition during cooling. By making these crystals exist in the slag, the powder slag film can be easily peeled from the mold.

  The calcium oxide crystals and / or dicalcium silicate crystals present in the cooled powder slag as a crystalline phase may be formed during melt cooling or may be unmelted.

  On the other hand, in the clothing ingot method, in order to form a powder slag film with molten powder slag, appropriate meltability and viscosity are required, and the viscosity of the molten powder slag at 1300 ° C. is 0.01 to 20.0 Pa. -It is desirable to be in the second range. If the viscosity at 1300 ° C. of the molten powder slag is less than 0.01 Pa · sec, the fluidity of the molten powder slag is too good to absorb the unevenness of the mold surface, and good slab surface properties cannot be obtained. Absent. If the viscosity of the molten powder slag at 1300 ° C. is higher than 20.0 Pa · sec, the flowability of the molten powder slag is poor and it is difficult to flow between the metal solidified shell and the mold. Since the properties cannot be obtained, it is not preferable. The viscosity of the molten powder slag at 1300 ° C. is more preferably in the range of 0.05 to 10.0 Pa · second.

For example, the composition of the powder for an ingot of the present invention is preferably adjusted to the following composition so as to satisfy the above-mentioned conditions. In addition, the composition of the powder for clothing lump is a composition represented by the oxide equivalent amount of the molten powder slag obtained by heating the powder for clothing lump to 1300 ° C:
CaO: 30 to 70 _wt%, SiO 2: 0 to 25 _{wt%, Al} 2 O 3: _{15~45 wt%, Na 2 O + Li 2} O + F + MgO: 10~30 wt%

  Here, CaO has a more preferable range of 35-65 mass%. If CaO is less than 30% by mass, the total amount of calcium oxide crystals and dicalcium silicate crystals is insufficient, such being undesirable. Moreover, when CaO exceeds 70 mass%, since melting | fusing point of the powder for clothing ingots will become high too much, and it will become insufficient melting, it is not preferable.

Further, SiO ₂ is more preferably in the range of 0 to 20 wt%. When SiO ₂ exceeds 25% by mass, the total amount of calcium oxide crystals and dicalcium silicate crystals is less than 5% by mass, which is not preferable.

Further, _Al 2 _{O 3} is more preferably in the range of 20 to 30 wt%. If Al ₂ O ₃ is less than 15% by mass, the melting point of the ingot powder is excessively high and is insufficiently melted. Further, when the Al ₂ O ₃ exceeds 35 wt%, the total yield of calcium oxide crystals and dicalcium silicate crystals unfavorably less than 5 wt%.

_{Further, Na 2 O + Li 2 O} + F + MgO is preferably in the range of 10 to 25 wt%. When Na ₂ O + Li ₂ O + F + MgO is less than 10% by mass, the melting point of the powder for ingots is excessively high and is not preferable because it is insufficiently melted. _Further, Na ₂ when O + Li 2 O + F + MgO exceeds 30 wt%, the total yield of calcium oxide crystals and dicalcium silicate crystals unfavorably less than 5 wt%.

  Furthermore, C can be contained in an amount of 15% by mass or less, preferably 10% by mass or less. C is a component for adjusting the melting rate of the powder for clothing ingot.

  In addition, Cr, P and / or B can also be blended in order to inhibit the phase transition of dicalcium silicate crystals and suppress powdering. When Cr, P and / or B are contained, the total thereof is preferably less than 1% by mass, more preferably less than 0.5% by mass.

  Furthermore, in addition to the above components, inevitable components derived from raw materials such as Fe, Ti, Mn, and S can be allowed for the powder for clothing ingots of the present invention.

  In addition, as a raw material of the powder for ingots of the present invention, for example, carbonates such as calcium carbonate, cements such as Portland cement and alumina cement, and various oxides and fluorides can be selected and used. For example, carbon raw materials such as carbon black and graphite can be used.

  In addition, the shape of the powder for an ingot of the present invention is not particularly limited, and for example, a powder form or a granule such as an extruded granule, a hollow spray granule, a stirring granulation granule, or a tumbling granulation granule is used. It can be changed according to the situation.

The following examples further illustrate the powder for ingots of the present invention.
Example 1
Tables 1 and 2 show powders for clothing ingots according to the present invention, and Table 3 shows powders for comparison. The “composition (mass%)” in the table is a composition expressed in terms of oxide equivalent of molten powder slag obtained by heating the powder to 1300 ° C.

Evaluation Method The powders of the product of the present invention and the comparative product were dissolved as follows:
An electric furnace was used for heating, the sample was loaded into a graphite crucible, and the crucible and the crucible were rapidly inserted into a furnace at 1300 ° C. The slag state is obtained by visually observing the appearance of the sample after heating at 1300 ° C. for 10 minutes and classifying it as follows. ○: Melt and flow, ×: Semi-molten or powder layer remains;
The state of slag collapse is heated at 1300 ° C. for 10 minutes and then visually observed after cooling to 25 ° C. over 10 hours, and is indexed as follows. 5: Pulverization, 4: Collapse, 3: Partially collapsed, 2: Crack generation, 1: No change, −: Not slag, evaluation not possible;
The viscosity is measured at 1300 ° C. by the platinum ball pulling method;
The crystal amounts of the calcium oxide crystal and the dicalcium silicate crystal are respectively determined by an internal standard method according to JIS K 0131 “General Rules for X-ray Diffraction Analysis”.

  All of the products of the present invention shown in Tables 1 and 2 showed appropriate slag formation and viscosity, had sufficient calcium oxide crystals and dicalcium silicate crystal amounts, and signs of slag collapse were observed.

In Comparative Example 1 shown in Table 3, since the amount of CaO was small, calcium oxide crystals and dicalcium silicate crystals did not precipitate, and no slag collapse was observed. Moreover, in the comparative example 2, since there was too much CaO amount, sufficient slag formation was not obtained. Furthermore, in Comparative Example 3, since the amount of SiO ₂ was too large, calcium oxide crystals and dicalcium silicate crystals did not precipitate, and no slag collapse was observed. In Comparative Example 4, since the amount of Al ₂ O ₃ was small, sufficient slag formation could not be obtained. Furthermore, in Comparative Example 5, since the amount of Al ₂ O ₃ was too large, sufficient calcium oxide crystals and dicalcium silicate crystals were not obtained, and slag collapse was not observed. In Comparative Example _6, since _{Na 2 O + Li 2 O +} F + MgO amount is small, sufficient slag is not obtained. Furthermore, in Comparative Example 7, since the amount of Na ₂ O + Li ₂ O + F + MgO was too large, sufficient calcium oxide crystals and dicalcium silicate crystals were not obtained, and slag collapse was not observed. Moreover, although the comparative example 8 is corresponded to the powder of patent document 3, decay | disintegration of slag was not recognized.

Example 2
Table 4 shows the results of use when 10 kg of the powder of the present invention or the comparative product was placed in the mold and about 10 tons of molten steel was poured down and cast. The slab was water-cooled by watering, and the slab surface was observed before the rolling process. The “carbon amount (mass%) of the raw powder” in Table 4 indicates the amount of carbon added to the powder base material in use.

Evaluation method Slag residue on the surface of the slab after cooling: Visual confirmation of presence or absence;
Slag removal work of the slab before rolling: whether or not grinding with a grinder was performed. -: Not implemented, ×: Implemented;
Slag inclusions after rolling: ・ Evaluate the number per slab after rolling. ◎: None, △: 1-5, ×: 6 or more

本発明品の衣造塊用パウダーは、いずれも実機にて鋳片冷却時にスラグの剥離が認められ、スラグの除去作業を必要とせず、圧延後においても介在物の発生は認められず良好であった。
これに対して、比較品５及び８のパウダーは、冷却後鋳片表面にスラグが残留しており、スラグ除去工程を経たものの、スラグ除去が十分ではなく、圧延後鋼片において介在物が発生した。

The garment ingot powders of the present invention were all good because slag peeling was observed when the slab was cooled in the actual machine, no slag removal work was required, and no inclusions were observed after rolling. there were.
On the other hand, the powders of comparative products 5 and 8 have slag remaining on the surface of the slab after cooling, and after the slag removal process, the slag removal is not sufficient, and inclusions are generated in the steel slab after rolling. did.

The powder for clothing ingots of the present invention contributes to simplification of operations in ingot casting and improvement of product quality by reducing inclusions, and can be suitably used as powders in various metal clothing ingot methods.

Claims (3)

In the powder for clothing lump, the composition represented by the oxide equivalent amount of the molten powder slag obtained by heating the powder for clothing lump to 1300 ° C. is CaO: 30 to 70 mass%, SiO ₂ : 0 to 25 _{mass%, Al} 2 O 3: _20~45 wt% and _{Na 2 O + Li 2 O +} F + MgO: 10 to 30 wt%, after heating and at 1300 ° C. 10 min, upon cooling to room temperature, cooling the molten powder slag A powder for clothing ingot, wherein calcium oxide crystals or dicalcium silicate crystals, or both of them are precipitated as a crystal phase.   The powder for clothing ingots according to claim 1, wherein the sum of the amounts of calcium oxide crystals and dicalcium silicate crystals is in the range of 5 to 20% by mass in the cooled molten powder slag. The powder for clothing ingots according to claim 1 or 2 , wherein the viscosity of the molten powder slag at 1300 ° C is in the range of 0.01 to 20.0 Pa · sec.